Browsing by Subject "DNA, Satellite"

Now showing 1 - 4 of 4
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    Alpha satellite DNA biology: finding function in the recesses of the genome.
    (Chromosome research : an international journal on the molecular, supramolecular and evolutionary aspects of chromosome biology, 2018-09) McNulty, Shannon M; Sullivan, Beth A
    Repetitive DNA, formerly referred to by the misnomer "junk DNA," comprises a majority of the human genome. One class of this DNA, alpha satellite, comprises up to 10% of the genome. Alpha satellite is enriched at all human centromere regions and is competent for de novo centromere assembly. Because of the highly repetitive nature of alpha satellite, it has been difficult to achieve genome assemblies at centromeres using traditional next-generation sequencing approaches, and thus, centromeres represent gaps in the current human genome assembly. Moreover, alpha satellite DNA is transcribed into repetitive noncoding RNA and contributes to a large portion of the transcriptome. Recent efforts to characterize these transcripts and their function have uncovered pivotal roles for satellite RNA in genome stability, including silencing "selfish" DNA elements and recruiting centromere and kinetochore proteins. This review will describe the genomic and epigenetic features of alpha satellite DNA, discuss recent findings of noncoding transcripts produced from distinct alpha satellite arrays, and address current progress in the functional understanding of this oft-neglected repetitive sequence. We will discuss unique challenges of studying human satellite DNAs and RNAs and point toward new technologies that will continue to advance our understanding of this largely untapped portion of the genome.
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    Genomic size of CENP-A domain is proportional to total alpha satellite array size at human centromeres and expands in cancer cells.
    (Chromosome Res, 2011-05) Sullivan, Lori L; Boivin, Christopher D; Mravinac, Brankica; Song, Ihn Young; Sullivan, Beth A
    Human centromeres contain multi-megabase-sized arrays of alpha satellite DNA, a family of satellite DNA repeats based on a tandemly arranged 171 bp monomer. The centromere-specific histone protein CENP-A is assembled on alpha satellite DNA within the primary constriction, but does not extend along its entire length. CENP-A domains have been estimated to extend over 2,500 kb of alpha satellite DNA. However, these estimates do not take into account inter-individual variation in alpha satellite array sizes on homologous chromosomes and among different chromosomes. We defined the genomic distance of CENP-A chromatin on human chromosomes X and Y from different individuals. CENP-A chromatin occupied different genomic intervals on different chromosomes, but despite inter-chromosomal and inter-individual array size variation, the ratio of CENP-A to total alpha satellite DNA size remained consistent. Changes in the ratio of alpha satellite array size to CENP-A domain size were observed when CENP-A was overexpressed and when primary cells were transformed by disrupting interactions between the tumor suppressor protein Rb and chromatin. Our data support a model for centromeric domain organization in which the genomic limits of CENP-A chromatin varies on different human chromosomes, and imply that alpha satellite array size may be a more prominent predictor of CENP-A incorporation than chromosome size. In addition, our results also suggest that cancer transformation and amounts of centromeric heterochromatin have notable effects on the amount of alpha satellite that is associated with CENP-A chromatin.
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    Telomere disruption results in non-random formation of de novo dicentric chromosomes involving acrocentric human chromosomes.
    (PLoS Genet, 2010-08-12) Stimpson, Kaitlin M; Song, Ihn Young; Jauch, Anna; Holtgreve-Grez, Heidi; Hayden, Karen E; Bridger, Joanna M; Sullivan, Beth A
    Genome rearrangement often produces chromosomes with two centromeres (dicentrics) that are inherently unstable because of bridge formation and breakage during cell division. However, mammalian dicentrics, and particularly those in humans, can be quite stable, usually because one centromere is functionally silenced. Molecular mechanisms of centromere inactivation are poorly understood since there are few systems to experimentally create dicentric human chromosomes. Here, we describe a human cell culture model that enriches for de novo dicentrics. We demonstrate that transient disruption of human telomere structure non-randomly produces dicentric fusions involving acrocentric chromosomes. The induced dicentrics vary in structure near fusion breakpoints and like naturally-occurring dicentrics, exhibit various inter-centromeric distances. Many functional dicentrics persist for months after formation. Even those with distantly spaced centromeres remain functionally dicentric for 20 cell generations. Other dicentrics within the population reflect centromere inactivation. In some cases, centromere inactivation occurs by an apparently epigenetic mechanism. In other dicentrics, the size of the alpha-satellite DNA array associated with CENP-A is reduced compared to the same array before dicentric formation. Extra-chromosomal fragments that contained CENP-A often appear in the same cells as dicentrics. Some of these fragments are derived from the same alpha-satellite DNA array as inactivated centromeres. Our results indicate that dicentric human chromosomes undergo alternative fates after formation. Many retain two active centromeres and are stable through multiple cell divisions. Others undergo centromere inactivation. This event occurs within a broad temporal window and can involve deletion of chromatin that marks the locus as a site for CENP-A maintenance/replenishment.
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    Telomere-to-telomere assembly of a complete human X chromosome.
    (Nature, 2020-09) Miga, Karen H; Koren, Sergey; Rhie, Arang; Vollger, Mitchell R; Gershman, Ariel; Bzikadze, Andrey; Brooks, Shelise; Howe, Edmund; Porubsky, David; Logsdon, Glennis A; Schneider, Valerie A; Potapova, Tamara; Wood, Jonathan; Chow, William; Armstrong, Joel; Fredrickson, Jeanne; Pak, Evgenia; Tigyi, Kristof; Kremitzki, Milinn; Markovic, Christopher; Maduro, Valerie; Dutra, Amalia; Bouffard, Gerard G; Chang, Alexander M; Hansen, Nancy F; Wilfert, Amy B; Thibaud-Nissen, Françoise; Schmitt, Anthony D; Belton, Jon-Matthew; Selvaraj, Siddarth; Dennis, Megan Y; Soto, Daniela C; Sahasrabudhe, Ruta; Kaya, Gulhan; Quick, Josh; Loman, Nicholas J; Holmes, Nadine; Loose, Matthew; Surti, Urvashi; Risques, Rosa Ana; Graves Lindsay, Tina A; Fulton, Robert; Hall, Ira; Paten, Benedict; Howe, Kerstin; Timp, Winston; Young, Alice; Mullikin, James C; Pevzner, Pavel A; Gerton, Jennifer L; Sullivan, Beth A; Eichler, Evan E; Phillippy, Adam M
    After two decades of improvements, the current human reference genome (GRCh38) is the most accurate and complete vertebrate genome ever produced. However, no single chromosome has been finished end to end, and hundreds of unresolved gaps persist1,2. Here we present a human genome assembly that surpasses the continuity of GRCh382, along with a gapless, telomere-to-telomere assembly of a human chromosome. This was enabled by high-coverage, ultra-long-read nanopore sequencing of the complete hydatidiform mole CHM13 genome, combined with complementary technologies for quality improvement and validation. Focusing our efforts on the human X chromosome3, we reconstructed the centromeric satellite DNA array (approximately 3.1 Mb) and closed the 29 remaining gaps in the current reference, including new sequences from the human pseudoautosomal regions and from cancer-testis ampliconic gene families (CT-X and GAGE). These sequences will be integrated into future human reference genome releases. In addition, the complete chromosome X, combined with the ultra-long nanopore data, allowed us to map methylation patterns across complex tandem repeats and satellite arrays. Our results demonstrate that finishing the entire human genome is now within reach, and the data presented here will facilitate ongoing efforts to complete the other human chromosomes.